Cryogenic liquid level control

ABSTRACT

A pneumatically operated automatic control for the liquid level of cryogenic liquids in which a start valve controls the starting of cryogenic liquid delivery which continues until the level of the cryogenic liquid reaches a temperature-sensitive sensor. A delivery valve for the cryogenic liquid is held open by a body of entrapped gas under pressure which is first pressurized by the start valve. A metering valve may be employed to release the entrapped gas at a predetermined rate to limit the duration of each filling cycle regardless of the height of liquid level reaches after operation of the start valve. A second temperatureresponsive means may be employed for operating the start valve to provide automatic incremental control of liquid level between minimum and maximum levels, and the delivery valve may be employed for controlling the main line valve where evaporative cooling in the main line valve has a tendency to condense pressurized gas at the control port of the line valve.

United States Patent Hedstrom [4 1 Feb. 1, 1972 [52] U.S.Cl. ..62/49,137/386 [5 1] Int. Cl. l7c 7/00 [58] Field of Search ..62/49; 9 H52;l37/386 389,

[56] References Cited UNITED STATES PATENTS 2,619,107 ll/l952 Graham2,756,765 7/l956 Agule et al.. .....l37/386 3,089,512 5/1963 Julien..9l/52 X 3,262,280 7/1966 Chaney ..62/49 FOREIGN PATENTS ORAPPLICATIONS 1,501,801 10/1967 France ..62/49 Primary Examiner-Robert G.Nilson Attorney-Limbach, Limbach 84 Sutton [57] ABSTRACT A pneumaticallyoperated automatic control for the liquid level of cryogenic liquids inwhich a start valve controls the starting of cryogenic liquid deliverywhich continues until the level of the cryogenic liquid reaches atemperature-sensitive sensor. A delivery valve for the cryogenic liquidis held open by a body of entrapped gas under pressure which is firstpressurized by the start valve. A metering valve may be employed torelease the entrapped gas at a predetermined rate to limit the durationof each filling cycle regardless of the height of liquid level reachesafter operation of the start valve. A second temperature-responsivemeans may be employed for operating the start valve to provide automaticincremental control of liquid level between minimum and maximum levels,and the delivery valve may be employed for controlling the main linevalve where evaporative cooling in the main line valve has a tendency tocondense pressurized gas at the control port of the line valve.

7 Claims, 5 Drawing Figures PATENTEU FEB 1 I972 sum 1 or- 3 INVENTORALBL'RT ll MOST/WM BY FIE--1- W M A TTUKNEVS PATENTED FEB 1 1972 sum 3or 3 INVENTOR. ALERT V. f/[DSTKUM CRYOGENIC LIQUID LEVEL CONTROL Thisinvention relates to an automatic liquid level control for controllingthe flow of cryogenic liquids such as liquid nitrogen from a pressurizedsupply of the liquid to a container while automatically controlling theliquid level between minimum and maximum levels. The device eliminateson and off chatter of the main dispensing valve by operatingincrementally to deliver a full stream of cryogenic liquid from the timea start valve is operated until the time that the liquid level in acontainer reaches a temperature sensor; after the liquid level hasreached the temperature sensor, further cryogenic liquid is notdispensed until the next operation of the start valve even if the liquidlevel falls below the temperature sensor.

In the preferred embodiment of the invention, the start valve isoperated automatically by a second temperature sensor which is set at aminimum level in a container to which the liquid level is permitted tofall.

The control apparatus of this invention operates by providing anentrapped body of pressurized fluid which is initially pressurized byoperation of the start valve and holds a delivery valve in a valve opencondition until the entrapped body of fluid is vented in response tooperation of the maximum level temperature sensor. Since the duration ofeach filling cycle is controlled by the time interval when the entrappedbody of fluid is contained, the maximum duration of each filling cyclemay be controlled by venting this entrapped body of fluid through ametering valve. The metering valve vent may be used with the high liquidlevel sensor to provide both time and liquid level controls on eachfilling cycle. The metering vent valve may also be used without the highliquid level sensor to provide time control on the filling cycle withoutmaximum liquid level control.

Many commercially available cryogenic liquid control valves developsubstantial evaporative cooling or cryosorbtion in the body of thevalve, particularly where the valve is installed between a pressurizedsupply of cryogenic liquid and a discharge nozzle which is open toatmospheric pressure. Where a main line valve of this type is employed,the main line valve does not function satisfactorily as the deliveryvalve of this invention because the evaporative cooling in the linevalve tends to liquify pressurized gas in the entrapped body of fluidholding the valve open so that the evaporative cooling dissipates thepressure of the entrapped fluid thereby closing the main line valveprematurely. The same result may occur with certain types of cryogenicliquid valves which provide an intentional leakage between the fluidpassages of the valve and the pressure control port of the valve.

In accordance with the preferred embodiment of this invention, adelivery valve is held open by the entrapped body of pressurized fluid,and the output of the delivery valve is connected to the control port ofone of these commercially available main line valves. Evaporativecooling in the main line valve has a tendency to liquify gas at thecontrol port of the main line valve, but pressure at the control port ofthe main line valve is maintained through the delivery valve. At thesame time, there is not sufficient flow of fluid through the deliveryvalve, with pressure differential across the delivery valve to providesufficient evaporative cooling in the delivery valve to liquify gas inthe entrapped body of pressurized fluid.

The control apparatus of this invention is operated in its entirety bypneumatic controls which may be integrated into a single control unit,and no electrical controls are provided which would require connectionto external power. The entire operating power for this apparatus isderived from the fluid pressure in the pressurized source of cryogenicliquid being dispensed together with the operating forces beingdeveloped by temperature responsive means which sense the liquid levelofa cryogenic liquid in a container being filled.

As indicated above, each incremental cycle of delivery of cryogenicliquid is instituted by operation of a start valve. The start valve maybe operated automatically by a minimum liquid level control sensor, butwhere this minimum liquid level control sensor is omitted, the identicalapparatus may be employed as a one-shot automatic filling control wherethe metering valve or the maximum level temperature sensor is employedfor automatically shutting off the delivery of liquid after initialdelivery of liquid is started manually be manual operation of the startvalve.

Other features and advantages of the invention will become apparent fromthe following description read in conjunction with the attached drawingsin which:

FIG. 1 is a schematic view of the preferred form of control apparatus ofthis invention illustrating that apparatus in the condition where theliquid level in a container has fallen part way from a maximum leveltoward a minimum level;

FIG. 2 is a view of the apparatus of FIG. 1 illustrating the conditionof the apparatus of FIG. 1 when the liquid level in the container firstfalls to the minimum level;

FIG. 3 is another view of the apparatus of FIG. 1 illustrating thecondition of the apparatus when the liquid level in the container risesto the maximum liquid level at the conclusion of an incremental fillingoperation;

FIG. 4 is a view similar to FIG. 2 but showing an alternative form ofthe apparatus employing an adjustable metering valve for venting theentrapped body of fluid, and;

FIG. 5 is a similar view of another alternative form of the inventionemploying a low-level liquid sensor for starting a filling cycle and theadjustable metering valve for ending the cycle regardless of the levelto which the cryogenic liquid rises.

Referring now in detail to the drawings and particularly to FIG. I, theapparatus therein illustrated is an automatic control for dispensingcryogenic liquids such as liquid nitrogen from a pressurized source 10of the liquid such as a conventional Dewar flask to a body of liquid 12in a container not shown. The source 10 has a delivery conduit 14,usually provided with a shutoff valve, and a branch line 16 is connectedto the supply conduit 14 through the pressure gauge 17. The deliveryconduit 14 of the supply 10 extends into the container 10 and to thebottom of the container so that pressure in the head space of thecontainer forces cryogenic liquid through the delivery conduit 14, andas the apparatus is illustrated in FIG. 1, the branch line 16 receivesliquid nitrogen from the main delivery conduit 14. In operation of theapparatus, cryogenic liquid entering the branch conduit 16 is generallyvaporized by the latent heat of the conduit 16 and thermal conductionaway from the conduit 16 since there is an insufficient flow of fluidthrough the conduit 16 to keep the temperature of the conduit 16 at theboiling point of the cryogenic liquid. Conventional containers like thecontainer 10 often include a second delivery conduit (not shown)communicating with the head space over the liquid in the container wherepressurized gas in the head space is impounded. Where such a containeris employed, the branch conduit 16 can be connected to the head space ofthe container instead of to the delivery conduit 14.

A main line valve 18 has a supply opening 20 connected to the conduit 14and a discharge opening 22 connected by a conduit 24 to a dischargenozzle 26. The line valve 18 is of the type mentioned above having abellows 28 engaging a valve stem 30 and a control port 32 wherepressurized fluid at the control port 32 causes the valve 30 to move toa valve open position, but cryogenic liquid flow through the valve,particularly where there is a pressure differential across the valve,causes sufficient evaporative cooling in the valve that pressurized gasbetween the control port 32 and the bellows 28 may be liquified.

A start valve 34 has a supply opening 36 connected to the branch line 16and a delivery opening 38 with a spring-loaded valve element 40 forclosing off the supply opening and a spring-loaded valve plunger 42extending through the body of the start valve 34 for opening the valveelement 40.

A temperature-responsive device comprising a bellows 44 and a capillarytube 46 is mounted adjacent to the body of the valve 34 so thatexpansion of the bellows 44 presses against the element 42 and opens thevalve 40. The bellows 44 and capillary tube 46 are a conventionalelement in which the bellows 44 may be made in a variety of shapes. Thelower end of the capillary tube 46 is sealed and forms a temperaturesensor, and the upper end of the capillary tube 46 communicates with theinterior of the bellows 44. The interior of the bellows 44 and theinterior of the capillary tube 46 are filled with a gas such as nitrogenor carbon dioxide which has a boiling point below ambient atmospherictemperatures but not lower than the boiling point of the cryogenicliquid 12 which is being sensed by the temperature responsive means.When the capillary tube 46 is not in contact with the cryogenic liquid12, the gas inside of the capillary tube 46 and bellows 44 vaporizesexpanding the bellows 44 to press upwardly on the element 42, and whenthe capillary tube 46 contacts the cryogenic liquid 12, the gas insidethe capillary tube liquifies creating a vacuum condition inside thebellows 44 which contracts the bellows It should be noted that theelement 42 which operates to unseat the valve 40 does not have any ventpassageway through it in contradistinction to valve elements describedbelow.

A high-level control valve 48 has a supply opening 50 connected byconduit 52 to the delivery opening of start valve 34. The valve 48 alsohas a delivery opening 54, valve stem 56 and a valve operator 58 similarto corresponding parts in the start valve 34. However, the valveoperator S8 is provided with an internal bore and lateral vent ports 60by which the interior of the valve 48 is vented when the valve operator58 is moved outwardly from the valve under the influence of its biasingspring. The high-level control valve 48 is operated by a bellows 62 andcapillary tube 64 similar in construction to the bellows and capillarytube 44 and 46 except that the capillary tube 64 is adjusted to bepositioned at the maximum level 66 to which cryogenic liquids are to befilled in the container whereas the capillary tube 46 is adjusted to theminimum level 68 to which the level of cryogenic liquid in the containeris permitted to fall.

A delivery valve 70 identical in construction to the valve 48 has supplyand delivery openings 72 and 74, respectively, connected respectively tothe branch conduit 16 and the control port 32 of the main line valve 18.

The delivery valve 70 is operated by expansion of a bellows 76, theinterior of which is connected by conduit 78 to the delivery port 54 ofthe high-level control valve 48.

The operation of the control apparatus of this invention will beapparent from sequential examination of FIGS. -l-3. FIG. 1 illustratesthe condition of the apparatus midway between two cycles of operation ofthe line valve 18. In this situation,.the

cryogenic liquid 12 has, at an earlier time, been filled to the highlevel 66 and has evaporated to some extent lowering the liquid level toa position midway between the high and low levels 66 and 68. In thissituation, the valve 34 is closed so that no pressure is applied tobellows 76 through valve 48 even though valve 48 is open. Since nopressure is applied to bellows 76, the delivery valve 70 is closedventing the control port 32 of main line valve 18 through the vent ports71 in the stem of delivery valve 70.

When at a later time, the cryogenic liquid 12 evaporates to the lowliquid level 68, the liquid in bellows 44 vaporizes expanding thebellows and opening valve 34. Valve 48 has already been opened, andaccordingly, pressurizedfluid flows from line 16 through valve 34, line52 and valve 48 to the bellows 76 opening the delivery valve 70. Whendelivery valve 70 opens, pressurized fluid flows from branch conduit 16through delivery valve 70 to the control port 32 of the main line valve18 opening main line valve 18 so that cryogenic liquid flows from thesupply through the main line valve 18 into the body of liquid 12 throughnozzle 26. As this cryogenic liquid flows, it may cause evaporativecooling in the main line valve 18 which may tend to liquify gas adjacentto the control port 32; however, this does not permit the main linevalve 18 to close since the control port 32 thereof is continuouslyrepressurized by fluid flowing thereto through the delivery valve 70from the branch conduit 16. This condition of the apparatus isillustrated in FIG. 2.

After a small amount of cryogenic liquid is delivered from the nozzle26, the level of cryogenic liquid rises to an intermediate level betweenthe levels 66 and 68 above the bottom of capillary tube 46 so that thestart valve 34 closes. At this time the high-level control valve 48 hasnot yet closed, and accordingly a body of pressurized fluid is entrappedin the interior of valve 34, the conduit 52, the interior of valve 48,and the interior of bellows 76. This body of entrapped pressurized fluidholds the delivery valve 70 open so that further dispensing of cryogenicliquid through the valve 18 continues.

When the level of cryogenic liquid [2 rises to the high level 66 asillustrated in FIG. 3, the bellows 62 contracts permitting the valve 48to close so that the interior of valve 48 is vented through the ventports 60 thereby permitting bellows 76 to contract venting the interiorof the delivery valve 70 so that valve 70 closes and pressure isrelieved from the control port 32 of main line valve 18 stopping anyfurther delivery of cryogenic liquid.

After this sequence of operation, further cryogenic liquid may boil offof the body of liquid 12 causing the bellows 62 to expand again to theoriginal condition illustrated in FIG. I, but since the conduit 52 isnot pressurized by the closed valve 34, no further dispensing ofcryogenic liquid will occur until the apparatus again assumes thecondition of FIG. 2.

It should be noted that the provision in this apparatus of a closed andtrapped volume of pressurized fluid in the conduit 52, bellows 76, andvalve 48 might provide a potential safety hazard where the apparatus isconstructed as illustrated in FIG. 1 with the branch conduit 16connected to a supply of cryogenic liquid rather than a supply ofpressurized gas. If this closed body of fluid were cryogenic liquidwhich boiled, the pressure in the closed system may rise substantially.In the apparatus of this invention, no safety hazard is provided sinceany rise in pressure in the closed cavity causes the pressure to riseinside valve body 34 so that the valve will be unseated venting excesspressure into the branch line 16. In this way, the fluid pressure in theentire system is limited substantially to the pressure in suppiy line14.

In the alternative form of apparatus shown in FIG. 4, an ad- 40 justableneedle valve vent 80 is provided in the conduit 52 for metering fluidout of the entrapped body of pressurized fluid at a predetermined ratedetermined by the setting of the needle valve. Where the needle valve isadjusted to a closed position merelypassing fluid through the conduit 52without venting it, the apparatus of FIG. 4 operates in exactly the sameway as the apparatus of FIGS. l-3. The same is true where the needlevalve is partially opened but not opened enough to dissipate thepressure in bellows 76 before the liquid level reaches capillary tube64;

When the valve 80 is further opened however, it acts as a timer controllimiting the duration of each filling cycle after the start valve 34 isoperated. In this situation, momentary opening of start valve 34provides an entrapped body of pressurized fluid in the interior of valve34, conduit 52, needle valve 80, valve 48, and bellows 76. Thispressurized body causes bellows 76 to expand with resulting delivery offluid through line 18, and fluid delivery continues until a sufficientamount of fluid is vented through needle valve 80 to permit bellows 76to contract and close valve 70.

A similar mode of operation occurs in the alternative form of apparatusshown in FIG. 5 where the conduit 52 containing the vent valve 80 isconnected directly to the bellows 76 omitting the high-level controlvalve 48 and its temperature sensor. The apparatus of FIG. 5 operatesautomatically to deliver a stream of cryogenic liquid to the body ofliquid 12 for a predetermined period of time without valve chatter everytime the liquid level falls below capillary tube 46, and the time periodfor liquid delivery, and hence the volume of liquid delivered, can beadjusted by adjusting needle valve 80.

While certain features of the invention and some illustrativeembodiments thereof have been illustrated and described in detail, it isobvious that many modifications thereof may be made without departingfrom the spirit and scope of the invention.

Iclaim:

1. Apparatus for dispensing cryogenic liquids from a pressurized supplysource of such liquids which comprises:

A. a pressure-responsive delivery valve having a discharge opening, asupply opening connected to said source, a control port, and means forconnecting said delivery opening to said supply opening when fluidpressure is applied to said control port;

B. a start valve having a supply opening connected to said supplysource, a discharge opening communicating with said control port of saiddelivery valve, and valve means movable between a valve open positionconnecting said supply and discharge openings and a valve closedposition disconnecting said supply and discharge openings withoutventing said discharge opening for establishing an entrapped body ofpressurized fluid between said start valve and said control port whensaid start valve closes after opening; and,

C. control means for venting said entrapped body of pressurized fluid;and

D. temperature-responsive means having a sensor adapted to be positionedat a minimum level in a container to which said container is to befilled with liquid with said temperature responsive means having movablemeans connected to the valve means of said start valve for moving thevalve means thereof to said valve closed position when the temperatureof said sensor is maintained at the temperature of a cryogenic liquid.

2. The apparatus of claim 1 in which said control means comprises anadjustable metering valve for delivering fluid from said entrapped bodyof pressurized fluid at a predetermined rate.

3. Apparatus for dispensing cryogenic liquids from a pressurized supplysource of such liquids which comprises:

A. a pressure-responsive delivery valve having a discharge opening, asupply opening connected to said source, a control port, and means forconnecting said delivery opening to said supply opening when fluidpressure is applied to said control port;

B. a start valve having a supply opening connected to said supplysource, a discharge opening communicating with said control port of saiddelivery valve, and valve means movable between a valve open positionconnecting said supply and discharge openings and a valve closedposition disconnecting said supply and discharge openings withoutventing said discharge opening for establishing an entrapped body ofpressurized fluid between said start valve and said control port whensaid start valve closes after opening; and,

C. control means for venting said entrapped body of pressurized fluid;

in which said control means comprises:

A. a high-level control valve having a supply opening connected to saiddischarge opening of said start valve, a discharge opening connected tosaid control port of said delivery valve, and valve means movablebetween a valve open position connecting said supply and dischargeopenings and a valve closed position closing said supply opening andventing said discharge opening, and;

B. temperature-responsive means having a sensor adapted to be positionedat a maximum level in a container to which said container is to befilled with liquid with said temperature-responsive means having movablemeans connected to said valve means of said high-level control valve formoving the valve means thereof to said valve closed position when thetemperature of said sensor is ture of said sensor is maintained at thetemperature of a cryogenic liquid whereby said apparatus will operateautomatically and incrementally to fill a container from said minimumlevel to said maximum level every time the cryogenic liquid level insaid container falls below said minimum level.

5. The apparatus of claim 4 in which each of said temperature-responsivemeans consists of a contractable bellows positioned to move the valvemeans of the valve operated by said temperature-responsive means, acapillary tube having a closed end forming said sensor and an open endcommunicating with the interior of said bellows, and a body of gasfilling said bellows and said capillary tube and having a boiling pointwhich is lower than ambient temperature, but not lower than the boilingpoint of said cryogenic liquid.

6. The apparatus of claim 5 characterized further by the inclusion of acryogenic liquid delivery conduit and a line valve having deliveryopening connected to said delivery conduit, a supply opening connectedto source, a control port connected to the discharge opening of saiddelivery valve, and means for connecting said delivery opening to saidsupply opening when fluid pressure is applied to said control portwhereby fluid pressure at the control port of said line valve is notdissipated by evaporative cooling in said line valve, and no evaporativecooling is applied to said delivery valve to dissipate fluid pressure atthe control port of said delivery valve.

7. Apparatus for dispensing cryogenic liquids from a pressurized supplysource of such liquid which comprises:

A. a pressure-responsive delivery valve having a discharge opening, asupply opening connected to said source, a control port, and means forconnecting said delivery opening to said supply opening when fluidpressure is applied to said control port;

B. a start valve having a supply opening connected to said supplysource, a discharge opening communicating with said control port of saiddelivery valve, and valve means movable between a valve open positionconnecting said supply and discharge openings and a valve closedposition disconnecting said supply and discharge openings withoutventing said discharge opening for establishing an entrapped body ofpressurized fluid between said start valve and said control port whensaid start valve closes after opening;

C. control means for venting said entrapped body of pressurized fluid;and

D. a cryogenic liquid delivery conduit and a line valve having adelivery opening connected to said delivery conduit, a supply openingconnected to source, a control port connected to the discharge openingof said delivery valve, and means for connecting said delivery openingto said supply opening when fluid pressure is applied to said controlport whereby fluid pressure at the control port of said line valve isnot dissipated by evaporative cooling in said line valve, and noevaporative cooling is applied to said delivery valve to dissipate fluidpressure at the control port of said delivery valve.

1. Apparatus for dispensing cryogenic liquids from a pressurized supplysource of such liquids which comprises: A. a pressure-responsivedelivery valve having a discharge opening, a supply opening connected tosaid source, a control port, and means for connecting said deliveryopening to said supply opening when fluid pressure is applied to saidcontrol port; B. a start valve having a supply opening connected to saidsupply source, a discharge opening communicating with said control portof said delivery valve, and valve means movable between a valve openposition connecting said supply and discharge openings and a valveclosed position disconnecting said supply and discharge openings withoutventing said discharge opening for establishing an entrapped body ofpressurized fluid between said start valve and said control port whensaid start valve closes after opening; and, C. control means for ventingsaid entrapped body of pressurized fluid; and D. temperature-responsivemeans having a sensor adapted to be positioned at a minimum level in acontainer to which said container is to be filled with liquid with saidtemperature responsive means having movable means conneCted to the valvemeans of said start valve for moving the valve means thereof to saidvalve closed position when the temperature of said sensor is maintainedat the temperature of a cryogenic liquid.
 2. The apparatus of claim 1 inwhich said control means comprises an adjustable metering valve fordelivering fluid from said entrapped body of pressurized fluid at apredetermined rate.
 3. Apparatus for dispensing cryogenic liquids from apressurized supply source of such liquids which comprises: A. apressure-responsive delivery valve having a discharge opening, a supplyopening connected to said source, a control port, and means forconnecting said delivery opening to said supply opening when fluidpressure is applied to said control port; B. a start valve having asupply opening connected to said supply source, a discharge openingcommunicating with said control port of said delivery valve, and valvemeans movable between a valve open position connecting said supply anddischarge openings and a valve closed position disconnecting said supplyand discharge openings without venting said discharge opening forestablishing an entrapped body of pressurized fluid between said startvalve and said control port when said start valve closes after opening;and, C. control means for venting said entrapped body of pressurizedfluid; in which said control means comprises: A. a high-level controlvalve having a supply opening connected to said discharge opening ofsaid start valve, a discharge opening connected to said control port ofsaid delivery valve, and valve means movable between a valve openposition connecting said supply and discharge openings and a valveclosed position closing said supply opening and venting said dischargeopening, and; B. temperature-responsive means having a sensor adapted tobe positioned at a maximum level in a container to which said containeris to be filled with liquid with said temperature-responsive meanshaving movable means connected to said valve means of said high-levelcontrol valve for moving the valve means thereof to said valve closedposition when the temperature of said sensor is maintained at thetemperature of a cryogenic liquid.
 4. The apparatus of claim 3characterized further by the inclusion of second temperature-responsivemeans having a sensor adapted to be positioned at a minimum level in acontainer to which said container is to be filled with liquid with saidtemperature-responsive means having movable means connected to the valvemeans of said start valve for moving the valve means thereof to saidvalve closed position when the temperature of said sensor is maintainedat the temperature of a cryogenic liquid whereby said apparatus willoperate automatically and incrementally to fill a container from saidminimum level to said maximum level every time the cryogenic liquidlevel in said container falls below said minimum level.
 5. The apparatusof claim 4 in which each of said temperature-responsive means consistsof a contractable bellows positioned to move the valve means of thevalve operated by said temperature-responsive means, a capillary tubehaving a closed end forming said sensor and an open end communicatingwith the interior of said bellows, and a body of gas filling saidbellows and said capillary tube and having a boiling point which islower than ambient temperature, but not lower than the boiling point ofsaid cryogenic liquid.
 6. The apparatus of claim 5 characterized furtherby the inclusion of a cryogenic liquid delivery conduit and a line valvehaving delivery opening connected to said delivery conduit, a supplyopening connected to source, a control port connected to the dischargeopening of said delivery valve, and means for connecting said deliveryopening to said supply opening when fluid pressure is applied to saidcontrol port whereby fluid pressure at the control port of said linevalve is not dissipated by evaporative cooling in said line valve, andNo evaporative cooling is applied to said delivery valve to dissipatefluid pressure at the control port of said delivery valve.
 7. Apparatusfor dispensing cryogenic liquids from a pressurized supply source ofsuch liquid which comprises: A. a pressure-responsive delivery valvehaving a discharge opening, a supply opening connected to said source, acontrol port, and means for connecting said delivery opening to saidsupply opening when fluid pressure is applied to said control port; B. astart valve having a supply opening connected to said supply source, adischarge opening communicating with said control port of said deliveryvalve, and valve means movable between a valve open position connectingsaid supply and discharge openings and a valve closed positiondisconnecting said supply and discharge openings without venting saiddischarge opening for establishing an entrapped body of pressurizedfluid between said start valve and said control port when said startvalve closes after opening; C. control means for venting said entrappedbody of pressurized fluid; and D. a cryogenic liquid delivery conduitand a line valve having a delivery opening connected to said deliveryconduit, a supply opening connected to source, a control port connectedto the discharge opening of said delivery valve, and means forconnecting said delivery opening to said supply opening when fluidpressure is applied to said control port whereby fluid pressure at thecontrol port of said line valve is not dissipated by evaporative coolingin said line valve, and no evaporative cooling is applied to saiddelivery valve to dissipate fluid pressure at the control port of saiddelivery valve.